Indeed his is, but no trainer in the world is going to make Justin Gatlin better than Usain Bolt, despite him being a professional athlete.
I can't speak specifically about Hart - because I don't know the facts of the matter and suspect none of us know them all (although some ITK's might know more than others).
But still, let's say Pep absolutely believes he can improve almost any player - if faced with no other option, then he'd probably do precisely that - made do with what he had, and rely entirely on squeezing the best out of what he had. But he's not in the position. He's in a position where he can choose better materials, and work on improving them instead - which in theory should give us a better end result. Pep could coach Benteke and make him better, or Messi and make him better. If he has the choice, he'll coach Messi. That may be the case with Joe.
My purely gut feeling is that there's more to it than one specific thing, but it's pure guess work. I would say 99% of the posts on this subject at pure guesswork too. It doesn't take a rocket scientist to come up with the line 'He clearly doesn't fit Pep's footballing philosophy' and make it sound informed, but in truth, it's no more valid a view than 'Hart's a bit of a bighead and probably rubs Pep up the wrong way'. The former sounds very informed and the latter sounds very simple, but either or both could be correct.
I definitely understand all that Hart's won and his CV is impressive, but the likes of Nicky Butt has 6 PL titles, 2 FA Cups and a CL winners medal. I wouldn't dream of swapping him for KdB though!
